1. Technical Field
The disclosure relates to the field of deep trench production in microelectronic component substrates.
2. Discussion of the Related Art
In the microelectronics field, trenches are commonly used to define a functional element by delimiting it spatially from the adjacent elements. Additive manufacturing techniques are used for example to produce the various layers of material forming the constituent parts of the unitary detection elements of a matrix sensor, or of storage transistors for example, and then each of the unitary elements is isolated from its neighbors by making trenches around it.
A trench is however a large source of defects, and, in the absence of any treatment of the sidewalls thereof, the lower the trench form factor, i.e. the ratio between the width and the depth thereof, the more degraded the operation of the components is generally observed to be.
Indeed, the sidewalls of a trench have a number of surface defects. For example, when the trenches delimit unitary detection elements, the result is a significant noise in the signal delivered thereby and a loss of quantum efficiency, which explains why the sidewalls of a trench are commonly subjected to a treatment, and in particular overdoping when the trench is produced in a semi-conductor substrate, made of silicon for example, and/or the deposition of a passivation layer.
Furthermore, there is a plurality of method types in existence for etching a trench. Etch methods that restrict the formation of surface defects, such as dry etching for example, may be used. This method type is however very slow, and therefore incompatible with the mass production of microelectronic components. Additionally, these methods do not result in trenches with a very low form factor.
Other etch method types, and in particular plasma-based ion etching, allow trenches to be etched quickly, and are therefore compatible with the mass production of components. However, this method type comprises etching the trench portion after portion by the sequential application of elementary deposition and etch cycles. The resulting sidewalls are very irregular with a large number of overhangs and notches. The overhangs, or projections, may block up to 20% of the width of a trench of less than one micrometer. The presence of such irregularities greatly restricts the subsequent treatment of the trench sidewalls since the overhangs mask part of the sidewalls. These masked parts are thus difficult to access in respect of the subsequent deposition of a passivation layer or the implementation of overdoping.
There is therefore a need for an etch method that will both produce deep trenches with very low form factors, and typically form factors below 1/25, and produce trenches which have sidewalls substantially free of surface defects, and in particular smooth, passivated sidewalls.